1. Field of the Invention
The present invention relates to both a method and an apparatus for three-dimensional photography, and specifically to a method in which both a camera and a lenticular screen move during a continuously scanning process and real-time combined 3-D static or animated photographs are produced.
2. Background of the Invention
We live in a three-dimensional (3-D) world. In this world, we see not only the height and width of an object, but also its depth. Traditional photography, however, produces only two-dimensional (2-D) photographs, i.e., photographs that only capture the height and width of an object. It has been a goal of many inventors for over a century to invent cameras that can take 3-D photographs.
The human visual system uses many visual cues to obtain 3-D perception. Visual disparity is the most effective of these cues. When we focus on an object, the two eyes look at it from different perspectives. The difference in perspective results in a slight difference in the images received by the two eyes, i.e., the right eye sees more of the right side of the object than the left eye, and vice versa. The human visual system possesses the ability to combine the two slightly different perspectives and extract the depth information (3-D) from the visual disparity of the corresponding image points. The principle of a 3-D camera is to produce images that carry information of visual disparity. When these images are viewed by human eyes, the visual disparity embedded in the images can be observed and thus the depth or 3-D sensation perceived.
There are several methods for making 3-D photographs. One method is binocular stereoscopic imaging, in which a pair of images is produced. The two images are taken from two spatially separated positions, either by two cameras or by one moving camera. The two images are then viewed through a device, which allows the observer to see the left image only with the left eye and the right image only with the right eye. The viewer's brain combines the two images into a single 3-D image. The viewing angle for a device using this method is very limited. An observer can properly view the 3-D image at only one viewing angle. If his eyes are moved away from the right position, the 3-D perception will be distorted or lost (see Ferwerda J. G., The World of 3-D: A practical guide to stereo photography, 1990, Borger: 3-D Book Productions).
Three-dimensional spatial imaging (also called autostereoscopy) is a significant improvement over binocular stereoscopic imaging. In autostereoscopy, several (more than two) images are taken and later combined to form one single 3-D image. Such an autostereoscopic image conveys much more information (dependent on the number of images combined) than that of a binocular stereoscopic image. An observer views such an image through a device such as a lenticular screen or a barrier screen. By changing his viewing angle, the viewer will get the impression of seeing the same object from different perspectives semi-continuously. This is similar to seeing an object in the real world (see McAllister D. F., Stereo Computer Graphics and Other True 3D Technologies, 25 1993, N.J.: Princeton University Press).
A simple method for taking autostereoscopic images is to use a multi-lens camera (with the lenses either in the same camera housing or in different camera housings), or a single camera placed in many different spatial positions. The multiple photographs are then combined in certain ways (either using an optical device or a computer) to form a single 3-D photograph. U.S. Pat. No. 5,337,096 and U.S. Pat. No. 4,800,407 disclose the kind of cameras used with this method. One of the major disadvantages about this method is that the 3-D perception of such an image is discontinuous: when an observer moves his head while viewing such a 3-D photograph, there is a noticeable jump from one image to the next. This jumpiness is due to the limited number of discrete images that are used to form the final photograph. Another disadvantage of the method is that the recorded 3-D image cannot be viewed directly from the developed image. In order to get a viewable 3-D image, a post-processing procedure (i.e., the combining process) must be done, which can be rather expensive and inaccurate.
A much better way to achieve autostereoscopy is to simulate the eye's view by continuously scanning the subject being photographed using a device employing a single-lens camera. The device possesses means for moving the camera in order to scan the subject being photographed over a continuously changing angle. The continuous scanning method greatly increases the information contained in the photograph, so that a photograph taken this way can produce strong 3-D perception. Such a scanning camera is usually combined with a lenticular screen or a barrier, placed close to the focal plane of the camera and in front of a photosensitive film used for recording images. The combination of a moving camera and a lenticular screen produces a 3-D photograph that can be viewed directly, without all the complex post-processing required in the multi-lens method.
U.S. Pat. No. 2,508,487 discloses a continuously moving camera structure and the method of using it. In this design the camera follows a path in a circular arc about a fixed center at which the subject is located. During the scanning process, the camera is always oriented towards the subject being photographed. A lenticular screen and a strip of film rotate around a vertical axis in synchronization with the camera during scanning of the image. The range of operation of this camera is limited because the distance between the subject being photographed and the camera is predetermined by the radius of the circular track, and is therefore fixed.
U.S. Pat. No. 4,107,712 describes another camera design and scanning method. In this design, the camera position is fixed throughout the scanning. A small aperture shutter, adjacent to a large lens, moves sideways during the exposure and scans the incoming light throughout the length of the lens in a horizontal direction. A lenticular screen moves a predetermined small distance along a linear path in the same direction as the moving shutter, relative to the static film and camera. The disadvantages of this method are: (1) it requires a large and high-quality lens, which is difficult and expensive to produce, (2) the scanning distance of the aperture is relatively small, hence the 3-D perception of a photographs taken by such a camera is weak, and (3) the relative small movement of the lenticular screen (about one pitch) requires a very precise motor control system. Small errors in movement of the elements during scanning can reduce the quality of the resulting 3-D photograph.